The present invention relates to a sealing arrangement for a multicoordinate sensing head of the type which includes a housing which defines an opening, and a sensing pin which defines an axial direction and includes a free end which extends out of the housing through the opening.
A wide variety of such multicoordinate sensing heads are disclosed in a number of publications. In large part, these publications are directed to mechanical details which relate to the construction of the multicoordinate sensing heads.
Thus, for example, German DE-OS No. 3 031 770, German patent DE-PS No. 23 47 633, British Pat. No. 1,237,813 and British Pat. No. 1,599,758 disclose sensing heads in which the opening at the bottom of the sensing head housing through which the sensing pin passes is covered by an elastic seal which takes the form of a folded bellows. This bellows is fastened at its outer edge to the sensing head casing, and at its inner edge to the sensing pin in order to cover the opening between the pin and the housing while accommodating angular movement of the sensing pin with respect to the housing. Typically, such bellows are made of rubber or of an elastomeric synthetic material in order to prevent the penetration of dust and moisture into the interior of the sensing head housing.
Such bellows seals are adequate in operation as long as the sensing heads are used in a benign environment such as that of a typical coordinate measuring machine. To an increasing degree, however, sensing heads are used on numerically controlled processing machines, and thus must operate in a much harsher environment which may, for example, include shavings or cuttings, cooling fluid and cutting oils. Bellows of the accordion type are in many cases unsuitable for use in such harsh environments since hot shavings or chips can damage or even destroy elastomeric accordion bellows.